Over the past decade, the demand for composite materials in the areas of transportation, building and storage, and various other industries has increased. This trend is a result of the flexibility and cost efficiency such systems offer relative to conventional products. For example, in transportation, panels used in semi-trailers, truck bodies, and portable storage containers have traditionally been fabricated from steel, aluminum, wood or fiberglass-reinforced materials. However, all-metal construction is expensive and heavy, and fiberglass and wood can gouge or splinter. Moreover, wood products such as plywood can delaminate or absorb moisture, potentially reducing the lifetime of the panel due to rotting. Similar problems are faced in the construction industry with the fabrication of structures using conventional products.
Composite systems offer the flexibility to combine the advantages of a variety of materials in their core and facing layers, so that products can be designed and fabricated to optimize price and performance. A wide variety of materials are available. For example, core materials can include products such as polypropylene or polyethylene-based materials, aluminum, styrofoam, paper and polycarbonate. Facing materials can include products such as fiberglass-reinforced plastic, metals such as stainless steel and aluminum, acrylonitrile-butadiene-styrene, and various other polymer products.
One challenge facing composite systems, however, is the need to bond the various layers together. This is particularly a concern when bonding adjacent dissimilar materials. For example, in multilayer films tie layers produced from adhesive composition layers are typically positioned between the dissimilar layers to be bonded, and the layers then adhered by conventional means.
Other applications require good adhesion between a metal and an adjacent layer. For example, nail guns often use nail-collation tape to load nails into the gun, where the nails are adhered to the tape using an adhesive layer. Still other applications include wire and cable, where an aluminum wire must be adhered to the outer layer of low density polyethylene. In composite multilayer pipe applications, an aluminum interior layer is often sandwiched between interior and exterior layers of polypropylene, polyethylene or cross-linked polyethylene. In these structures, adhesive composition layers are required between the polyolefins and aluminum.
Various adhesive compositions have been proposed. For example, functionalized polyolefins have been combined with a base polymer and poly(isobutylene) or high ethylene content materials such as ethylene-propylene copolymers or ethylene-propylene-diene terpolymers, for example as described in U.S. Pat. Nos. 4,087,587, 4,298,712, 4,487,885, 4,774,144, and 5,367,022. However, a continuing need exists for compositions providing superior levels of adhesion for today's demanding applications. It has unexpectedly been found that compositions comprising a blend of an ethylene copolymer of butene and a propylene-based polymer; a polyolefin grafted with an ethylenically unsaturated carboxylic acid or acid derivative; and an olefin polymer resin different than the ethylene copolymer of butene, the propylene-based polymer and the grafted polyolefin, exhibits superior adhesion performance.